Let the goose hunt begin!
Noticed this sign being put up instore in the Redruth Extra so asked at the desk. They only had 2 of the White Mario Kart 7 bundles which I've bought for my 2 boys for Christmas.
The poster does say in the bottom left that the promotion starts on 4th April 2016...so possibly old promotional stock.
This is not the NEW 3DS XL, but the older version.